Forget football. Never has a thread been more designed for me. Depends how heavy you want to go, you've got old school heavy metal (Black Sabbath), 80s Thrash (Metallica - Megadeth), more 'modern' stuff (Machine Head, Mastodon, Trivium), and the very heavy black/death metal (Arch Enemy, Cannibal Corpse) - if you're new to the genre I would recommend working your way forward from the earlier stuff I mentioned at the start. There's a whole host of other sub-genres within it all but you're going down the rabbit hole if you go down that route.

What kinda stuff/bands have you dabbled with before when in the gym etc?

If you're looking at 80s thrash metal then Reign In Blood by Slayer is a mighty fine way to pass half an hour.

My Dying Bride is one of my favourite bands, a wonderful blend of Death/Gothic/Doom metal; Opeth take Death Metal and give it a touch of Prog Rock treatment, Orchid and Morningrise are highly recommended.

Emperor is a pretty good Black Metal band (Anthems To The Welkin At Dusk and In the Nightside Eclipse get regular airings through the Briston_Addick speakers); although often poo-pooed by Black/Extreme Metal die-hards, Cradle Of Filth also get my vote with Dusk ... And Her Embrace as their best album in my opinion.

A bloody good (and, at times, fun) sub-genre is Folk Metal (I've been overdosing on this recently ). The style of metal varies from band to band: genre pioneers Skyclad combined old-school metal with folk, whilst Irish band Cruachan mix Black metal influences with traditional Celtic melodies. Scandinavia and Finland is a particularly good source of Folk Metal, Finntroll, Korpiklaani, and Moonsorrow being personal favourites. Edit: forgot to include Ensiferum - bloody idiot.

Yeah. It depends how heavy you want it really. Anaal Nathrakh or Nasum are a hell of a long way from Deep Purple.

Maybe Pantera or Machine Head to start? Both are fairly heavy, accessible and good for adrenaline. 'Vulgar Display of Power' and 'Burn My Eyes' are 2 genre classics, not a filler song between them.

If you like that but it's perhaps not quite enough, go for Slayer (Reign in Blood, as my learned friend Briston says) and see where that takes you. It might be noise or you might absolutely bloody love it and open your ears even further.

Speaking of Japan, if you want a change of pace from hairy blokes shouting at you, why not try some of the 'girls metal' bands from Japan. They're usually at the melodic power metal end of the scale. Bands like Lovebites, Aldious, Mary's Blood and Lightbringer are easier on the ears (and eyes) and they have some amazing vocalists and ridiculously skillful guitarists.